There are many industrial and medical applications which utilize gas spectrometers to monitor the presence and concentration of one or more predefined components in a gas sample. In this regard, light of a known spectral content may be directed on an optical pathway through a gas sample and the intensity of the transmitted light may be detected at a number of different center-wavelengths. By utilizing known light absorption characteristics of the predefined gas components at the center-wavelengths, the detected light intensities provide a basis to determine, via statistical processing, the concentrations of the predefined components.
As will be appreciated, it is important that initial calibration conditions within a spectrometer be maintained in order to accurately relate measured light intensities to gas component concentrations in use. This is particularly true in respiratory gas spectrometers used to measure the concentration of oxygen, CO.sub.2 and/or one or more anesthetic agents such as nitrous oxide, halothane, enflurane, sevoflurane, desflurane and isoflurane in a respiratory gas stream. In such applications, a separate sample stream is typically drawn from a patient respiratory gas assembly and directed into a gas sample chamber that is positioned on the optical pathway between the light source and detector. If there are variations along the optical pathway utilized in the respiratory gas spectrometer which have arisen since calibration (e.g. contamination of the gas sample chamber), such variations may lead to an inaccurate concentration determination.
Further, in order to provide a highly robust respiratory gas spectrometer, it is important that the transmitted radiation from the gas sample chamber yield a sufficiently high signal-to-noise ratio at the detector. This is particularly important when an array of detector elements are simultaneously illuminated by the transmitted radiation. By way of primary concern, the signal-to-noise ratio may unacceptably decrease as the radiation source employed in the spectrometer ages.